Process for producing high-porosity non-evaporable getter materials

ABSTRACT

A process is disclosed for producing non-evaporable getter materials having high porosity and improved gas sorption rates. The process includes mixing together a metallic getter element, a getter alloy and a solid organic compound, all three components being in the form of powders having specific particle sizes. The mixture is subjected to a compression of less than about 1000 kg/cm 2  and is sintered at a temperature between about 900° C. and about 1200° C. for a period between about 5 minutes and about 60 minutes. The getter material thus obtained is used to produce getter bodies shaped as pellets, sheets or discs having better mechanical strength than similar bodies of other getter material having comparable porosity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.08/820,555, filed on Mar. 19, 1997, which in turn is acontinuation-in-part of U.S. application Ser. No. 08/792,794, filed onFeb. 3, 1997, and U.S. application Ser. No. 08/477,100, filed on Jun. 7,1995 now abandoned, the disclosure of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to field of getter materials. Inparticular, the present invention relates to processes for makingnon-evaporable getter materials having a very high porosity and to thegetter materials thus obtained.

2. The Relevant Art

Non-evaporable getter materials (known in the art as "NEGs") are widelyused for creating and maintaining high vacuum conditions. Suchconditions are required commonly for devices such as thermal insulators,lamps and in semiconductor processing chambers. These materials also areused for the purification of gases for application in processesrequiring gases of high purity such as semiconductor manufacturingprocesses. Common NEG materials include metals such as zirconium (Zr),titanium (Ti), niobium (Nb), tantalum (Ta), vanadium (V) and theiralloys. The alloys can include additional elements, such as aluminum(Al) and/or iron (Fe), for example, the alloy having a weight percentagecomposition Zr 84%-Al 16% which is manufactured and sold by SAES®Getters S.p.A. (Lainate, Italy) under the tradename St 101 or the alloyhaving a weight percentage composition Zr 70%-V 24.6%-Fe 5.4%, alsomanufactured and sold by SAES® Getters under the tradename St 707.

Getter materials act by chemisorption of gases such as carbon monoxide(CO), carbon dioxide (CO₂), water (H₂ O), molecular oxygen (O₂), andmolecular hydrogen (H₂). Apart from H₂, which dissociates and diffusesinside the getter material even at low temperatures, the other gasesremain chemisorbed on the surface of the getter material overtemperatures which range from about 200° C. to about 500° C., dependingon the NEG material. The diffusion of the chemisorbed species into thematerial occurs at higher temperatures.

The surface characteristics of the NEG material play a fundamental rolein the sorption of reactive gases. A large specific surface (surface perunit weight) of the material and access of the gases to the surface ofthe NEG material are parameters of fundamental importance to theperformance of the NEG. These parameters would be optimized by the useof NEG materials in the form of powders, but powdered NEG materialscannot be used in practice. Rather, the powder NEG materials either arecompressed into pellets which are sintered to impart mechanicalstrength, loaded and compressed in open containers, or rolled onto asupport. Regardless of the form employed, the compression and/or heatsintering operations reduce the specific surface of the NEG materialswith respect to the starting powder. Moreover, most of the getterparticles reside within the interior bulk of the sintered gettermaterial where the gases to be sorbed have only limited access with aconsequential decrease in the sorption capacity of the device and in thegas sorption rate.

German Patent Application DE-A-2,204,714 discloses a method forpreparing porous NEG devices based on metallic zirconium. According tothis method, graphite powder is added to the zirconium powder, alongwith a third organic component, for example ammonium carbamate, whoseweight may reach the total weights of the zirconium and graphite. Duringthe heat sintering treatment the organic component evaporates, leaving aporous structure consisting of zirconium and graphite which acts as ananti-sintering agent for zirconium; thus preventing an excessivereduction in the specific surface of the zirconium.

However, the above-cited German patent application refers only to theuse of elemental components and does not mention the use of alloys.Also, the organic component is added in the form of powder ofmillimeter-sized grains. Due to the large grain size of the organiccomponent, the final getter device has a high porosity with respect toits geometric volume. The porosity distribution obtained, however, isdoes not enhance access of gases to the surface of the internal NEGmaterial grains. Furthermore, the materials thus prepared have poormechanical properties.

British Pat. GB-2,077,487 discloses a porous NEG material obtained froma powder mixture of a metallic getter material, such as titanium orzirconium, and the previously mentioned St 707 alloy as ananti-sintering agent. According to the disclosure, the particles ofmetallic material have a size of about 125 μm, while the particles ofthe St 707 alloy have a size of less than 400 μm but are larger than thesize of the metallic component. The patent specification states that theratio of the sizes of the two components is selected so as to prevent anexcessive sintering of the metal during the heat treatment, which wouldlead to a reduction of the specific surface and consequently to a lowerefficiency of the resulting getter device. The use of an organiccomponent is not discussed.

Finally, U.S. Pat. No. 4,428,856 discloses a porous NEG materialcontaining from 50% to 98% titanium by weight, from 1.5% to 30% of ahigh melting point metal selected from among niobium, tantalum,molybdenum (Mo) and tungsten (W), and from 0.5% to 20% of titaniumhydride (TiH₂). This patent states that zirconium powders are readilyflammable and explosive, whereby one of the objects of the patent is toprovide a getter composition that avoids the use of zirconium.

The porosity and specific surface characteristics of the above-describedporous NEG materials, though improved with respect to the conventionalNEGs, still are not sufficient for particular applications, such assmall-volume getter pumps where high performance is required of thegetter material. Thus, it would be advantageous to provide porous NEGsthat have good mechanical strength and improved porosity and specificsurface characteristics.

SUMMARY OF THE INVENTION

The present invention provides getter materials and getter bodies havingthe combined properties of good mechanical strength, high porosity andhigh specific surface characteristics. Thus, the present inventionprovides getter materials and getter bodies that can be employed inapplications requiring high-performance gettering, such as themaintenance of vacuum states using small volume getter pumps.

In one aspect, the present invention provides a method for making anon-evaporable getter material. The method of the invention includesproviding a powder mixture that includes a metallic getter elementhaving a grain size smaller than about 70 μm; and at least one getteralloy having a grain size smaller than about 40 μm. Also included in themixture is an organic component which is a solid at room temperature andhas the characteristic of evaporating at 300° C. substantially withoutleaving a residue on the grains of either the metallic getter element orthe getter alloy when the materials forming the mixture are sintered. Inaddition, the organic powder has a particle size distribution such thatabout half of its total weight consists of grains smaller than about 50μm, the remainder of the grains being between about 50 μm and about 150μm in size. The powder mixture is then subjected to compression at apressure less than about 1000 kg/cm² to form a compressed powdermixture. The compressed powder mixture is sintered at a temperaturebetween about 900° C. and about 1200° C. for a period of between about 5minutes and about 60 minutes. During the sintering, the organiccomponent evaporates from the compressed powder mixture substantiallywithout leaving a residue on the grains of the metallic getter elementand the getter alloy to form thereby a network of large and small poresin the getter material.

In one embodiment, the weight ratio between the metallic getter elementand the total amount of getter alloy is between about 1:10 and about10:1. In another embodiment, the weight ration is between about 1:3 andabout 3:1. In another embodiment, the weight of the organic compoundconsists of up to about 40% of the overall weight of the powder mixture.In some embodiments, the getter alloy used is a Zr-containing orTi-containing binary or ternary alloy. In one particular embodiment, thegetter alloy is a Zr--V--Fe tertiary alloy having a weight percentagecomposition of Zr 70%-V 24.6%-Fe 5.4% and the metallic getter element iszirconium. In another particular embodiment, a second getter alloy isincluded that has a strong hydrogen gettering capacity. In oneembodiment, the second alloy is a Zr--Al alloy, and in a still moreparticular embodiment, the alloy is one having the percentage weightcomposition Zr 84%-Al 16%.

In another aspect the present invention includes getter bodies formedfrom the getter material resulting from the process of the invention. Inone embodiment, the getter body is formed into a pellet, a sheet or adisc. These materials can be used in high vacuum getter pumps forachieving high vacuum states in semiconductor processing chambers. Thus,in another aspect, the present invention includes methods and apparatusfor fabricating semiconductor devices under a high vacuum.

These and other aspects and advantages of the present invention willbecome more apparent when the Description below is read in conjunctionwith the accompanying Drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a shows a microphotograph obtained with a scanning electronmicroscope (SEM), magnification×700, of a getter material of theinvention whose preparation is described in Example 1. FIG. 1bshows adrawing reproducing the microphotograph of FIG. 1a. The black areas ofFIG. 1b correspond to regions of St 707 alloy, the gray areas to regionsof Zr and the white areas to pores of large size (denoted "1") and poresof smaller size (denoted "2").

FIG. 2a shows a SEM microphotograph, magnification×700, of a gettermaterial whose preparation, described in Example 2, following theprocedures described in DE-A-2,204,714 cited above. FIG. 2b shows adrawing reproducing the microphotograph of FIG. 2a. In FIG. 2b, theblack areas correspond to regions of graphite and the gray areas toregions of Zr.

FIG. 3a shows a SEM microphotograph, magnification×700, of a gettermaterial prepared as described in Example 3 according to the proceduresdescribed in GB-2,077,487 cited above. FIG. 3b shows a drawingreproducing the microphotograph of FIG. 3a. The black areas of FIG. 3bcorrespond to regions of St 707 alloy, the gray areas to regions of Zr.

FIG. 4a shows a SEM microphotograph, magnification×700, of a comparativegetter material obtained according to the process described in Example4. FIG. 4b shows a drawing reproducing the microphotograph of FIG. 4a.In FIG. 4b, the black areas correspond to regions of graphite and thegray areas to regions of Zr.

FIG. 5a shows a SEM microphotograph, magnification×700, of a comparativegetter material obtained according to the process described in Example5. FIG. 5b shows a drawing reproducing the microphotograph of FIG. 5a.The black areas of FIG. 5b correspond to regions of St 707 alloy, thegray areas to regions of Zr.

FIG. 6a shows a SEM microphotograph, magnification×700, of a gettermaterial of the invention whose preparation is described in Example 6.FIG. 6b shows a drawing reproducing the microphotograph of FIG. 6a. InFIG. 6b the black areas correspond to regions of St 101, the grayregions correspond to regions of St 707, and the lighter areas toregions of Zr.

FIG. 7 shows a graph of the gas sorption characteristics of the fivesamples of getter material of FIGS. 1-6. The CO sorption rate (S),measured in cubic centimeters of absorbed CO per second per gram ofgetter material ##EQU1## is given as a function of the amount ofabsorbed CO (Q) measured in cubic centimeter.torricelli per gram ofgetter material (cc.torr/g).

FIG. 8 shows the nitrogen sorption curves for the same samples used withrespect to the data shown in FIG. 7.

FIG. 9 shows the hydrogen sorption curves for a material of theinvention and a comparison material.

FIGS. 10a, 10b, 10c, and 10d illustrate some possible shapes of getterbodies which can be obtained using the getter material of the presentinvention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

In one aspect, the present invention provides getter materials havingnovel structural and functional characteristics that provide excellentgettering performance. In particular, the getter materials of thepresent invention include a unique network of pores that imparts to thegetter materials of the invention high porosity and surface area inaddition to good mechanical strength.

As seen in FIGS. 1a and 1b, the getter materials of the inventioncomprise a porous internal structure including a first network of largediameter pores 1 providing gas molecules access to the internal portionsof the getter material. The first network of pores is combined with asecond network of smaller diameter pores 2 that provide access to thesurfaces of the single grains of the components which comprise thegetter material. From the combination of these two pore networks highvalues of porosity and surface area, together with good mechanicalstrength, are imparted to the getter materials of the invention as willbe described in greater detail below. This unique structure is obtainedby sintering a metallic getter element, a getter alloy and an organicsolid as described herein.

In one embodiment, the components of the getter materials of theinvention comprise a metallic getter element in combination with agetter alloy. The metallic getter element may be any of the elementalmetals employed in the field, such as, but not limited to, zirconium(Zr), titanium (Ti), niobium (Nb), vanadium (V) and tantalum (Ta). Amongthese titanium and zirconium are preferred. The metallic getter elementcan be employed in the form of a fine powder having a particle sizesmaller than about 70 μm. In one embodiment, the particle size isbetween about 40 μm and about 60 μm.

The getter alloy can be a titanium-based getter alloy that optionallycan be combined with one or more transition elements. Alternatively, azirconium-based alloy, such as, for example, the binary alloys Zr--Al,Zr--V, Zr--Fe and Zr--Ni, or ternary alloys, e.g., Zr--Mn--Fe orZr--V--Fe can be used. The Zr--V--Fe alloys are described in U.S. Pat.No. 4,312,669 to Boffito, et al., which is incorporated herein byreference. The use of the Zr--V--Fe tertiary alloys is preferred, and inparticular the above-mentioned St 707 alloy, having a weight-basedpercentage composition Zr 70%-V 24.6%-Fe 5.4%. The latter alloy isavailable commercially from SAES® Getters S.p.A. (Lainate, Italy).According to one embodiment of the present invention, the getter alloyis employed in the form of a powder having a maximum particle sizesmaller than about 40 μm. In another embodiment the particle size issmaller than about 30 μm.

In some embodiments at least a second getter alloy is included. In oneparticular embodiment, the second getter alloy is chosen from amongthose getter alloys displaying a strong gettering capacity for hydrogen.Such getter alloys are especially useful in applications where hydrogenis a component of the gas being evacuated as hydrogen sorption by manygetter materials is reversible; thus leaving a residual partial pressureof hydrogen in the chamber to be evacuated. In particular, difficultiesin obtaining a desired degree of vacuum can arise where a first getteralloy is chosen that is effective for gettering gases other thanhydrogen, but which has poor sorption characteristics for hydrogen.However, gettering alloys having a strong gettering capacity forhydrogen can be included with the first getter alloy to reduce thehydrogen partial pressure in the chamber beyond that possible with thefirst getter alloy alone. Particular examples of such strong hydrogengetters include, but are not limited to, alloys of Zr and Al, and, moreparticularly, the alloy having the weight percentage composition Zr84%-Al 16% which is sold commercially under the tradename St 101 also bySAES® Getters S.p.A.

The weight ratio between the metallic getter element and the totalamount of getter alloy can vary over a wide range. In one embodiment,the ratios of the metallic getter element and getter alloy are betweenabout 1:10 and about 10:1. In another embodiment this ratio is betweenabout 3:1 and about 1:3. Amounts of the metallic element higher thanthose indicated above may result in decreased gettering efficiency,whereas the use of excessive amounts of the getter alloys may causedifficulties in sintering the getter bodies obtained from the powdercompression, possibly leading to poor mechanical strength.

In one embodiment, the organic compound used in the formation of thegetter materials of the invention is a solid at room temperature that iscapable of evaporating without leaving significant residues on thegrains of either the metallic getter element or the getter alloy whenthe components are sintered to form the getter material of theinvention. In one embodiment, the organic compound is capable ofevaporating as described above at temperatures lower than about 300° C.,so as not to generate vapors which may react at the temperatures atwhich the getter materials become active. Some examples of organicmaterials meeting having these characteristics include, but are notlimited to, ammonium oxalate, ammonium benzoate and ammonium carbamate.These materials are available commercially, e.g., from Aldrich ChemicalCo. (Milwaukee, Wis.).

According to one embodiment of the invention, the organic compound isemployed in the form of a powder. In another embodiment, this powderincludes equal portions of particles having a particle size smaller thanabout 50 μm and particles having a size between about 50 μm and about150 μm. The weight of the organic compound can be as much as 40% of thecombined weights of the metallic getter element and getter alloy powdersdescribed above. In one embodiment, the weight of the organic compoundis between about 10% and about 35% of the combined weights of themetallic getter element and the getter alloy prior to sintering. If toolittle of the organic compound is employed, the getter device obtainedupon sintering may lack significant porosity; whereas if the amount oforganic compound used is greater than about 40% by weight, the getterbodies obtained may lack mechanical stability.

Prior to sintering, the powder mixture is subjected to a lightcompression at a pressure less than about 1000 kg/cm². In oneembodiment, the compression is at a pressure between about 50 kg/cm² andabout 800 kg/cm². Using less pressure may produce a final sintered bodyhaving a poor mechanical strength, whereas employment of a greaterpressure may cause excessive powder compaction reducing the specificsurface and, more importantly, reducing the porosity of the getter body.After compression, the powder mixture undergoes a heat treatment in aninert atmosphere or, more preferably, under vacuum, at a temperaturebetween about 900° C. and about 1200° C. In one embodiment thetemperature is maintained between about 1000° C. and about 1100° C. fora time between about 5 minutes and about 60 minutes.

The getter materials obtained according to the process of the presentinvention can be employed in any application requiring the presence of agetter material, for example: in lamps, thermally insulating interspaces(e.g. in thermos bottles) or semiconductor processing chambers tomaintain a vacuum (e.g., in semiconductor manufacturing processes suchas disclosed in U.S. patent application Ser. No. 08/332,564, theentirety of which is incorporated herein by reference), or in thepurification of gases. The getter materials of the present invention canbe formed into a variety of shapes and configurations to form getterbodies as will apparent to those having skill in the art. A possibleshape of a getter body suitable for the use in thermos bottles is, forexample, a pellet, as shown in FIG. 8a.

The functional characteristics of the getter materials of the inventionhave particular advantages to applications requiring high gas sorptionperformance with small-volume devices, for example, in small getterpumps. These types of getter pumps are disclosed, for example, in U.S.Pat. Nos. 5,324,172 and 5,320,496. The first of the above-cited twopatents discloses a getter pump made with sheet-shaped getter bodiesradially arranged around the pump axis. A possible sheet of gettermaterial to be used in this pump is shown in FIG. 8b. The second patentdiscloses a pump in which the getter bodies are shaped as stacked discsarranged coaxially to the pump body. Possible alternative shapes ofdiscs to be used in a pump similar to that of U.S. Pat. No. 5,320,496,in addition to those described in said patent, are shown in FIGS. 8c and8d.

Other getter pumps that can be used with the materials and devicesdescribed herein are described in co-pending U.S. patent applicationSer. Nos. 08/332,564; 08/348,798; 08/521,943; and 60/015,466, each ofwhich is incorporated herein by reference in its entirety and for allpurposes. The cited patent applications disclose inter alia variousgetter pump configurations in which discs of porous, sintered gettermaterial, such as fabricated using the methods and materials of thepresent invention, are supported on a support element and aresubstantially shielded from thermal contact with surrounding surfaces ina semiconductor processing chamber to achieve high vacuum conditions insemiconductor processing chambers for the production of semiconductordevices.

EXAMPLES

The following examples describe specific aspects of the invention toillustrate the invention and aid those of skill in the art inunderstanding and practicing the invention. However, these examplesshould not be construed as limiting the invention in any manner.

Example 1

This example relates to the preparation of a getter material of theinvention.

A mixture was prepared comprising about 2.4 g of metallic zirconiumhaving a particle size between about 40 μm and about 50 μm, about 3.6 gof St 707 alloy having a particle size smaller than about 30 μm andabout 4.0 g of ammonium carbamate in two equal portions of about 2 geach, one portion having a particle size smaller than about 50 μm andthe other portion of between about 50 μm and about 150 μm, usingstandard methods. The mixture was homogenized in a V-shaped mixer forabout 4 hours and compressed under about 150 kg/cm² of pressure. Thecompacted mixture was then sintered in a vacuum furnace by heating overa period of about 2 hours to about 1,050° C. and maintaining thematerial at that temperature for about 30 minutes. The getter materialthus prepared is referred to herein as Sample 1.

Example 2 Comparative

This example describes the preparation of a getter material according tothe process described in German Patent Application DE-A-2,204,714.

A mixture of about 5.8 g of metallic zirconium having a particle sizesmaller than about 44 μm, about 1.2 g of graphite powder having aparticle size between about 75 μm and about 128 μm, and about 3 g ofammonium carbamate powder having a grain size of about 1 mm was preparedusing standard methods. The mixture was homogenized as in Example 1 andsintered by heating to 1,050° C. over a period of about 55 minutes andmaintaining it at that temperature for about 5 minutes. The sinteredgetter body so prepared is referred to herein as Sample 2.

Example 3 Comparative

This example describes the preparation of a porous getter materialaccording to British Patent GB-2,077,487.

A mixture of about 4 g of metallic zirconium powder having a particlesize smaller than about 44 μm and about 6 g of St 707 alloy having aparticle size between about 53 μm and about 128 μm was prepared usingstandard methods. The mixture was homogenized as in the precedingexamples and sintered by following the same heat treatment as in Example2. The getter body thus obtained is referred to herein as Sample 3.

Example 4 Comparative

The preparation of a getter material according to the procedure ofExample 2 was repeated but using a finer grain ammonium carbamatepowder, with a grain size smaller than about 44 μm. The getter body thusobtained is referred to herein as Sample 4.

Example 5 Comparative

The preparation of a getter material according to the procedure ofExample 3 was repeated but wherein the powder mixture was compressed ata pressure of about 70 kg/cm² prior to sintering. The getter body thusobtained is referred to as Sample 5.

Example 6

This example relates to the preparation of a getter material of theinvention.

A mixture of about 35 g of metallic zirconium having a particle size ofbetween about 40 μm and about 50 μm, about 15 g of St 707 alloy having aparticle size lower than about 30 μm, about 50 g of St 101® alloy havinga particle size lower than about 30 μm, about 13 g of ammonium carbamatehaving a particle size less than about 50 μm, and about 20 g of ammoniumcarbamate having a particle size between about 50 μm and about 150 μmwas prepared using standard methods. The mixture was homogenized in aV-shaped mixer for about 4 hours; about 1.3 g of the homogenized mixturewas compacted by subjection of the mixture to compression at about 600Kg/cm² compression. The compacted mixture was then sintered by heattreatment in a vacuum furnace by heating to a temperature of about 1050°C. over a period of about 2 hours and by keeping it at that temperaturefor about 30 minutes. The getter body thus prepared is referred to asSample 6.

Example 7

Measurement of the gas sorption rate and capacity was carried out onSamples 1-5 at room temperature, after activation of the Samples byheating the Samples to about 600° C. for about 10 minutes using standardmethods. The gas sorption rate measurements were made by monitoring thetime required for each sample to absorb the measured amounts of gasduring a series of releases of gas into the test chamber, according tothe method described in ASTM F 798-82. The test gas employed was CO. Theresults of the tests are shown in the graph of FIG. 7 with curveslabelled 1-5 corresponding to each of Samples 1-5, respectively.

Example 8

A measurement of the sorption characteristics of Samples 1-5 was carriedout under the same conditions as in Example 6 using nitrogen as the testgas. The results are shown in FIG. 8.

Example 9

A measurement of the hydrogen sorption rate and capacity was carried outon samples prepared as described in Example 6 above (invention) andExample 2 above (comparative) at room temperature, after activation atabout 600° C. for about 30 minutes. The test was carried out accordingto the methods described in the ASTM F 798-82 standard. The results ofthe tests are shown in the graph of FIG. 9 as curves 6 and 7 for the twosamples prepared as described in Example 6 and Example 2 respectively.

Example 10

A measurement of the surface area for each of Samples 1-6 was performedaccording to the well-known B.E.T. method using a commercially availableQuantasorb QS-12 instrument. The results of this test are summarized inTable 1 below.

Example 11

The apparent density and the porosity P for each of Samples 1-6 wasdetermined. The apparent density is calculated as the ratio between theweight of a sample and its geometric volume. The term porosity indicatesthe percent value of porosity as calculated using the following formula:##EQU2## where d_(app) is the above-defined apparent density of thesample and d_(t) is the sample's theoretical density. The value of d_(t)is calculated from the known absolute densities and weight fractions ofthe materials making up the sample using the following formula: ##EQU3##where: d_(A) is the density of the first material making up the sample;

d_(B) is the density of the second material making up the sample;

d_(C) is the density of the third material making up the sample;

X_(A) is the weight fraction of the first material making up the sample

X_(B) is the weight fraction of the second material making up thesample; and

X_(C) is the weight fraction of the third material making up the sample.

The results are shown in Table 1 below.

                  TABLE 1                                                         ______________________________________                                                Surface Area                                                                              Apparent Density                                            Sample (m.sup.2 /g) (g/cm.sup.3) Porosity (%)                               ______________________________________                                        1       0.17        1.85        71.1                                            2 0.19 1.43 70.8                                                              3 0.08 5.07 20.8                                                              4 0.17 1.46 70.2                                                              .sup. 5.sup.\ N/A 6.10 4.70                                         6 0.19 2.10 63.9                                                            ______________________________________                                         .sup.\ The surface area of Sample 5 was below the sensitivity       threshold of the instrument and is assumed to be lower than the value of      0.08 m.sup.2 /g determined for Sample 3.                                 

The process for preparing comparative Sample 4 is a variation of theprocess of Example 2 wherein use is made of ammonium carbamate having aparticle size smaller than that of Example 2 and comparable to theparticle size of the ammonium carbamate used in the process of theinvention. Similarly, the process for preparing the comparative Sample 5is a variation of the process of Example 3, wherein the powder mixtureis lightly compressed as in the process of the invention.

As may be noted by examining the microphotographs shown in FIGS. 1-6,Samples 1 and 6, corresponding to a getter materials of this invention,have very different pore structures from those of prior art comparativeSamples 2-5. Specifically, the getter devices of the invention have porestructure which consist of macroporosities 1 permeating the sample bodyand microporosities 2 between the zirconium and alloy grains whereasSamples 2-5 all appear to have much less developed pore networks.

Table 1 shows that the comparative Samples 2 and 4 have specific surfaceand porosity values comparable to those of Samples 1 and 6, whereasSamples 3 and 5 have specific surface and porosity much lower thanSamples 1 and 6. On the other hand, Samples 2 and 4 have poor mechanicalstrength, are friable and lose particles easily, making these materialsunusable in certain technological applications.

In addition to this improved combination of structural and mechanicalcharacteristics, Samples 1 and 6 of the invention have the best gassorption characteristics of all of the samples tested, as may be notedby examining the graphs of FIGS. 7-9 wherein the sorption curves at roomtemperature of Samples 1-6 are given, respectively, for CO and N₂ andH₂. Sample 1 exhibits much higher sorption for both gases than eitherSample 3 or 5 which have less porous structures. Sample 1 also exhibitsbetter sorption capacity for both gases than either Samples 2 or 4, bothof whose porosity characteristics more similar to those of Sample 1.Sample 6 shows the same desirable properties of Sample 1 (i.e., goodmechanical strength, high porosity, and large specific surface) inaddition to strong hydrogen sorption capability. It will also be seenfrom FIG. 9 that Sample 6 has stronger hydrogen sorption capabilitiesthan Sample 2, although these materials have similar porosities. Acomparison of the getter bodies of the invention with the variouscomparative materials shows that the getter bodies of the inventioncombine the best mechanical and structural characteristics of thecomparative materials while offering the best sorption properties.

Finally, a comparison between the sorption characteristics of Samples 2and 4 and of Samples 3 and 5 shows that only getter materials producedusing the process of the invention can achieve the excellent resultsdescribed above. In fact, an examination of these Figures reveals thatby changing the preparation of Sample 2 (the process according to GermanPat. Application No. DE-A-2,204,714) in accordance with the process ofthe invention, i.e. by using ammonium carbamate having finer particlesize (Sample 4), the gas sorption characteristics worsen. Similarly, achange in the process for preparing Sample 3 (the process of accordingto British Pat. No. GB-2,077,487) by applying a light compression to thepowder mixture in accordance with the process of the invention (Sample5), also leads to a worsening of the gas sorption characteristics.

In conclusion, the tests show that the Samples prepared according to themethod of the invention exhibits the best gas sorption characteristicstogether with good mechanical strength, making them suitable fortechnological applications. As can be seen from the discussion of thepreparation parameters discussed above, this combination ofcharacteristics depends on the particular process, characterized by thecombination of its parameters, and does not derive merely from simpleparameter changes of known processes.

Although certain embodiments and examples have been used to describe thepresent invention, it will be apparent to those having skill in the artthat various changes can be made to those embodiment and/or exampleswithout departing from the scope or spirit of the present invention. Forexample, it will be appreciated from the foregoing that many othergetter alloys can be combined with the materials described herein toproduce getter materials having desirable performance. Also many othermetallic getter elements can be employed with the present invention, ascan other organic materials having the properties described above. Inaddition, those of skill in the art will appreciate that the gettermaterials and getter bodies of the invention can be used in allapplications requiring a getter material. In particular, the gettermaterials and getter bodies of the invention can be employed withelectron tubes (e.g., fluorescent lamps), thermally insulating jackets(e.g., refrigerator panels) and semiconductor processing chambers. Inaddition, the getter bodies of the invention can be formed into avariety of configurations for use in getter pumps.

What is claimed:
 1. A method for producing a semiconductor device undera high vacuum, comprising the steps of:a) producing a high vacuum in asemiconductor processing chamber using a non-evaporable getter materialprepared according to a process including the steps of:i) providing apowder mixture including:a) a metallic getter element having a grainsize smaller than about 70 μm; b) at least one getter alloy having agrain size smaller than about 40 μm; and c) an organic component whichis solid at room temperature and has the characteristic of evaporatingat 300° C. substantially without leaving a residue on the grains of saidmetallic getter element and said getter alloy when said metallic getterelement, said getter alloy and said organic component are sintered toform said getter body; and wherein said organic component has a particlesize distribution such that about half of its total weight consists ofgrains of size smaller than about 50 μm the remainder of said grains ofsaid organic component having a size between about 50 μm and about 150μm; ii) subjecting said powder mixture to compression at a pressure lessthan about 1000 kg/cm² to form a compressed powder mixture; and iii)sintering said compressed powder mixture at a temperature between about900° C. and about 1200° C. for a period of between about 5 minutes andabout 60 minutes wherein said organic component evaporates from saidpowder mixture substantially without leaving a residue on said grains ofsaid metallic getter element and said getter alloy to form thereby anetwork of large and small pores in said getter body; and b) processinga semiconductor wafer in said processing chamber to produce at least onesemiconductor device.
 2. A process according to claim 1, wherein theweight ratio between the metallic getter element and the getter alloy isbetween about 1:10 and about 10:1.
 3. A process according to claim 1,wherein the weight ratio between the metallic getter element and thegetter alloy is between about 1:3 and about 3:1.
 4. A process accordingto claim 1, wherein said getter alloy is a Ti-based or Zr-based getteralloy including at least one transition element or Al.
 5. A processaccording to claim 4, wherein said getter alloy is an alloy of Ti or Zrand a transition element.
 6. A process according to claim 5, whereinsaid getter alloy is selected from the group consisting of Zr--Al,Zr--V, Zr--Fe, and Zr--Ni.
 7. A process according to claim 4, whereinsaid getter alloy is an alloy of Ti or Zr and two transition elements.8. A process according to claim 7, wherein said getter alloy isZr--Mn--Fe, or Zr--V--Fe.
 9. A process according to claim 8, whereinsaid getter alloy which is a Zr--V--Fe tertiary alloy having a weightpercentage composition of Zr 70%-V 24.6%-Fe 5.4%.
 10. A processaccording to claim 4, wherein said powder mixture comprises a firstgetter alloy selected from the group consisting of alloys including Zrand at least one transition element and alloys including Ti and at leastone transition element, and a second getter alloy which has a stronghydrogen gettering capacity.
 11. A process according to claim 10,wherein said second getter alloy is an alloy of Zr and Al.
 12. A processaccording to claim 11, wherein said second getter alloy has thecomposition by weight of Zr 84%-Al 16%.
 13. A process according to claim1, wherein the metallic getter element is zirconium.
 14. A processaccording to claim 1, wherein the organic component is ammoniumcarbamate.
 15. A process according to claim 1, wherein the powdermixture is compressed with a pressure between about 50 kg/cm² and 800kg/cm².